1. Field of the Invention:
The invention relates to the field of evaporative fluid conditioning. More specifically, the invention relates to the field of sensible cooling of fluids (gas, liquid or mixtures with and without phase changes) to substantially the dew point for gas by indirect evaporative cooling within a heat exchanger having canalized gas and fluid flows and a lateral temperature gradient across the heat exchange plates.
2. Description of the Prior Art
Indirect evaporative cooling is a method of cooling a gas stream, usually air, by evaporating a cooling liquid, usually water, into a second air stream while transferring heat from the first air stream to the second. The method has certain inherent advantages compared to conventional air conditioning: low electricity requirements, relatively high reliability, and the ability to do away with the need for refrigerants such as R-134 and all the disadvantages they entail. However, indirect evaporative cooling is as yet only used in specially built commercial applications, and is not yet available on the market as a residential or after market product. This is due to certain disadvantages of known indirect evaporative coolers and methods: excessive cost, ineffective thermodynamic cycle that does not allow for enough cooling of air for the expenses involved, ineffective water supply system, scale buildup, poor or expensive heat exchanger, excessive pressure drop, difficulty approaching the dew point of the air stream (the theoretical limit of cooling), relatively high dew points in humid atmospheres, large pressure drops across the heat exchange apparatus, large heat exchange apparatus, and in some designs, reliance on a good deal of ancillary equipment.
U.S. Pat. No. 4,002,040 issued to Munters et al on Jan. 11, 1977 discloses a heat exchanger in which there is no mixing between canalized air streams, and in which the air stream passing through the device is put through a 270 degree turn within the device, resulting in a large pressure drop engendered by the flow path. Additionally, Munteres does not allow for cooling fluids other than outside air and cannot be used in applications where recirculation is desired.
U.S. Pat. No. 5,187,946 issued to Rotenberg et al on Feb. 23, 1993, discloses a heat exchanger having perforations through the heat exchange plates and alternating wet and dry channels. The applicant herein disputes the validity of the U.S. patent as it was based on applicant's Russian patent and disclosed more than a year before the U.S. patent was filed, as well as the Rotenberg patent is invalid as it copied the Russian patent, yet does not disclose the earlier patent or the true inventor, V. Maisotsenko. The present invention is different in substantial ways from the U.S. Pat. No. 5,187,946 disclosure (Maisotsenko Russian Patent 2046257) does not use a separate treatment of product fluids (cooled fluids, whether gas, as U.S. Pat. No. 5,187,946's disclosure is limited to, or other fluids), the thin plastic plates that operate as efficient heat transfer from dry channels to wet channels yet do not transfer heat laterally along the surface or the plates, or a shallow slope to the heat exchange plates to allow efficient wicking action, but instead discloses a relatively high angle. It also does not reveal use of a feeder wick, instead using complex and costly spray heads located in each wet channel. Finally, U.S. Pat. No. 5,187,946 argues against the use of channel guides, urging that turbulent flow provides better efficiency. However, this does not allow U.S. Pat. No. 5,187,946 to control the lateral temperature profile of the individual heat exchange plates. In addition by separating the working air stream from the product the working air decreases in flow as it passes through the channel perforations, reducing its pressure drop and at the same time allowing better control of the exhaust channels. This patent, similar to Munters above is limited to cooling outside air.
U.S. Pat. No. 5,170,633 issued to Kaplan on Dec. 15, 1992, shows the amount of ancillary equipment which can proliferate in indirect evaporative systems. U.S. Pat. Nos., 5,727,394, 5,758,508, 5,860,284, 5,890,372, 6,003,327, 6,018,953, 6,050,100, issued to Belding et al and Goland et al, display the same syndrome of excessive air treatment equipment. In examining systems such as those referred to, it should be borne in mind that a single additional heat exchanger adds more than one third to the overall cost of the system.
These systems, aside from the different methods again only apply for cooling air.
U.S. Pat. No. 5,453,223, dated Sept. 26, 1995, and nominally issued to the present applicant, discloses an apparatus in which alternating sets of wet and dry plates provide two streams of air: one dry, cooled by contact with the plates beside it, and one wet, cooled by direct evaporation. However, the unit requires two gas flows in and two gas flows out. In addition, the design in question does not provide for indirect cooling only, without additional direct evaporative cooling. While such a second stage of direct evaporative cooling, raising the humidity of the product air, is often desirable, it is as often not desirable.
Two pending applications by the present inventor also address the technology of indirect evaporative cooling. PCT Application PCT/US01/04082, filed Feb. 7, 2001, discloses one method of eliminating a second stage of direct evaporative cooling. PCT Application PCT/US01/04081 filed on Feb. 7, 2001, discloses better methods of design of the heat exchange cores of indirect evaporative coolers, allowing better wetting and reduced pressure drops.
An indirect evaporative method and apparatus providing more efficient air flow and heat transfer is desirable.